In the mushroom industry a mushroom bed having compost in caked form is used for growing the mushroom. During a stage in the mushroom growing a digger is conventionally used which includes tines mounted on a rotating shaft. The digger is moved from one end of the bed to another to work the compost so that it will be in a condition to receive a supplement. Generally, the supplement is in powder form and is manually applied to the worked bed. The fact that reliance must be had on manual labor to perform the supplement application has a number of drawbacks. This form of supplement application is costly because of the time required for the workers to apply the supplement. In addition, since unskilled workers are generally used for this task, the manner of applying the supplement can be inconsistent in that various areas require uniform application and certain areas require more application than adjacent areas. For example, the center of the bed would generally require a greater application. With conventional application techniques the desired manners of application might not be achieved. Additionally, when unskilled labor is used for applying the supplement waste occurs from, for example, spillage. The conventional manner of digging and then having manual application of the supplement is also disadvantageous in that it leads to high air conditioning costs in order to maintain the proper temperature.